Wind turbines are commonly prone to strikes from lightning. On the one hand, this may be caused because the wind turbine is installed at an exposed site which itself is prone to strikes from lightning. On the other hand, the wind turbine as such comprises a considerable extension in vertical direction, i.e. in the direction of the gravitational force of the wind turbine. This extension in vertical direction may be considerably greater than surrounding buildings and/or trees, such that lightning strikes more likely the wind turbine than the buildings and/or trees in the surroundings.
If lightning strikes a wind turbine, often the rotor blades of the wind turbine are hit. This is due to the fact that for horizontal axis wind turbines with at least three rotor blades the tips of the respective rotor blades typically represent the highest points or sections of the wind turbine above the ground. Consequently, the rotor blade, in particular the tip section of the rotor blade, is susceptible and vulnerable to lightning strikes.
In the state of the art lightning protection arrangements often comprise a lightning receptor which is integrated in the shell of the rotor blade and which is connected by an electrically conducting material with a lightning conductor. The lightning conductor is arranged and prepared for transmitting the electrical current from the lightning strike to the ground. Such a conventional lightning receptor is typically made of a material with a high electrical conductivity and has a size of a few centimeters. It might be slightly exposed relative to the surface of the shell of the rotor blade, although from an aerodynamic point of view a complete integration of the lightning receptor into the blade shell is preferred.
A disadvantage of conventional lightning protection arrangements is that despite the presence of a lightning receptor at a prominent and susceptible position on the rotor blade a considerable amount of lightning strikes hits the rotor blade at a distance away from the lightning receptor. This may cause considerable damage to the rotor blade, in particular to the shell of the rotor blade, which might be made of fiber composite material. Damages to the rotor blade due to lightning strikes reach from minor damages which do not need instantaneous repair over more serious damages of the shell of the rotor blade, which need timely repair in order to avoid that water or dust enters the inner structure of the rotor blade, and reach until grave damage of the rotor blade necessitating a shutdown of the wind turbine.
A conventional wind turbine lightning protection system is, for instance, disclosed in the international patent application WO 2012/055418 A1. Therein, a plurality of vortex generators, which are attached on a vortex generator strip, are connected by a conductive band to the receptor of a lightning protection system. This is an improvement compared to the conventional basic system of just having a lightning receptor incorporated into the shell of the rotor blade in so far as the lightning is able to strike any point along the electrically conductive vortex generator strip and is subsequently conducted to the lightning receptor. However, this lightning protection arrangement requires the provision of a vortex generator strip or at least of an electrically conductive band in the vicinity of the lightning receptor. Furthermore, there is still a considerable probability that lightning strikes or hits the rotor blade at a distance away of the conductive band or the vortex generator strip.
Thus, it would be desirable to provide a lightning protection arrangement and a method of avoiding that lightning hits and damages the rotor blade for a wind turbine which is improved compared to the state of the art. Thus, a reduction of the rate of lightning strikes hitting the rotor blade at a distance away of the lightning receptor could be achieved.